I got clean from various drugs almost two and a half years ago and I had this problem. I hadn't read for a very long time, and I was told that it would take up to or over two years to really get normal again. My head was in a cloud for the first six months, I was unable to read or retain anything I did read, I would forget things the second I read them. The next six months I started reading quite a bit, but had a lot of difficulty still, understanding sentences, especially those that didn't explain themselves well. My mind was very foggy still, but I was able to get through some of the older fantasy I used to read, stuff that was very story driven and I could get by without retaining everything. After a year clean, I petered off a bit, I seemed to have a lot of trouble again and for the next six or eight months I think I read one book. Then about six months ago I started writing again, and with that I began to read, tentatively. I picked up two books I had already read while clean, Patrick Rothfuss' Kingkiller Chronicles and breezed through those with ease. I had already forgotten them nearly completely from reading them a year and a half before. I started picking at things a bit more difficult, like Robert Heinlein's Stranger in a Strange Land and Aldous Huxley's Brave New World and even Michael Chabon's Adventure's of Kavalier and Clay (which was too difficult at the time). While these were certainly more difficult and tedious, I was able to get through them. I heard about Kurt Vonnegut and read Slaughterhouse Five, and fell absolutely in love. His writing was simple to read, easy to retain and still possessed enough clever intellectualism that it made me have to think about what I was reading and not just mindlessly read. As of now, I have little trouble read, I mean my mind is not the same as it once was, and it fills me with a lot of regret, but I make do. These are some books I have been reading or started reading recently to continue getting myself back on track.

Cat's Cradle

Breakfast of Champions

Ender's Game

For Whom The Bell Tolls

Starship Troopers

Childhood's End

The Count of Monte Cristo

Hopefully you can find something to bring you back on track. My suggestion, and my *tl;dr Read something simple and story driven. *